This invention concerns a direct reduction device to obtain metal iron with a high content of carbon in the form of iron carbide. The device is of, the gravitational type and comprises a reduction and carburation reactor under which a cooling and passivation container is arranged wherein the iron carbide is cooled and completely passivated.
Methods for the direct reduction of mineral iron which have been known and developed during the last fifty years require an integrated system with two fundamental units to obtain highly metallized iron.
In the first unit, called the reduction reactor, a reduction gas, generally hydrogen, carbon monoxide or a mixture of the two, is brought into contact, at high temperature, with the mineral iron.
The second unit, called the reformer, is to generate the reducing gas; here, natural gas is made to react with a gas containing oxygen, water vapor and/or carbon dioxide, generating a gas which is rich in hydrogen and carbon monoxide and which is injected into the reduction reactor.
In the last twenty years, auto-catalytic processes have been developed, wherein the metal iron is employed as a catalyser in the reforming reactions, and corresponding methods for the direct reduction of mineral irons, which eliminate the need for separate reaction units and the use of nickel catalysers, and also additional processing units.
More recently, auto-catalytic processes have been orientated towards the production of iron carbide starting from mineral irons in a single reactor, that is, of a single unit in which the steps of reduction, generation of reducing gas, carburation of the metal iron, cooling and passivation of the product all occur.
These devices with a single unit have at least the following two disadvantages however: during cooling and passivation, a column of gas rises towards the carburation zone, so that it is easy to lose control of the carbon and its transformation into iron carbide, given that it is not possible to control the optimum temperature level at which the carbon is diffused and combined; moreover, in order to ensure that the material remains for a suitable time in the carburation zone, it is necessary to increase the height of the column of material inside the reactor, so that the product is subjected to high pressure in the lower zone of the reactor itself, with the danger that the material deteriorates and fine particles are produced.
The present Applicant has devised, designed and perfected the direct reduction device according to the invention to overcome the shortcomings of the state of the art.
The direct reduction device to obtain iron carbide from oxides containing iron according to the invention is set forth and characterized in the main claim, while the dependent claims describe other innovative aspects of the invention.
One purpose of the invention is to achieve a device wherein the reaction steps, such as the direct reduction of the metal iron oxides and the carburation thereof, the passivation and cooling treatment are physically separate.
In accordance with this purpose the device according to the invention essentially consists in connecting a normal reduction reactor, in which metal iron is produced from mineral iron and consequent carburation, with a controlled atmosphere container to obtain the passivation and cooling of the product.
To be more exact, the device comprises a reduction, carbon deposit and carburation assembly, consisting of a reactor with an inlet from the upper portion for mineral containing iron oxides, a cylindrical reduction zone to reduce the metal iron oxides and to deposit the carbon above the iron, and a carburation zone, wherein the different carbides are formed: FeC, Fe2C, Fe3C, preferably Fe3C.
The reactor has a conical zone in the lower portion, where an increase in the hot iron carbide occurs. The conical zone is connected at the lower cart with a container by means of a valve for solids, normally hot.
The reactor also comprises a double injection of the reduction gas in order to effect a better distribution and supply of heat energy and a methane distributor, located just underneath the double injection of the process gas, in order to obtain the carbon deposit. All the gas which is generated in the carbon deposit zone and in the reduction zone rises towards the top of the reactor, that is, towards the inlet of the iron oxide.
The hot iron carbide between about 550xc2x0 C. and 650xc2x0 C. is transferred to the cooling container, where it is then passivated and cooled to about 50xc2x0 C. The material is then discharged by means of a vibrating feed assembly, with a grid or pendulum bar.